The present invention relates in general to vehicle speed control systems and in particular to an improved electronic system for automatically maintaining the actual speed of a vehicle at or near a predetermined desired speed, which system utilizes both analog and digital memory circuits.
Electronic vehicle speed control systems are well known in the art and are generally available most modern vehicles, either as original equipment or as an aftermarket addition. Such speed control systems are provided to automatically maintain the actual speed of the vehicle at or near a predetermined desired speed selected by the vehicle operator. Typically, electrical signals representing the actual and desired speeds of the vehicle are generated by the system and are supplied to a comparison circuit. The comparison circuit determines whether the actual speed of the vehicle is greater than, less than, or approximately equal to the desired speed and generates electrical control signals in accordance therewith. The control signals are fed to an actuating mechanism which is mechanically connected to the vehicle engine throttle. The actuating mechanism automatically regulates the position of the vehicle engine throttle in response to the control signals so as to increase, decrease, or maintain the actual speed of the vehicle. In this manner, the actual speed of the vehicle is maintained at or near the desired speed.
As such electronic vehicle speed control systems have been developed, they have been provided with certain features which provide the vehicle operator with additional ease and flexibility during use. One such feature is commonly referred to as the resume feature. The resume feature is utilized to engage the system to automatically return the actual speed of the vehicle to a prior desired speed after the system has been disengaged for some reason. For example, when a particular desired speed has been set by the vehicle operator and the system is engaged for normal operation, the actual speed of the vehicle will be maintained at or near that desired speed. If the brakes of the vehicle are applied by the operator, however, the system will become disengaged for obvious safety reasons. The resume feature permits the operator to thereafter re-engage the system to automatically return the actual speed of the vehicle to the prior desired speed simply by manipulating a single control switch of the system. Thus, a system offering the resume feature must include some means for storing the value of the prior desired speed when the system is disengaged so that the actual speed can be compared thereto upon activation of the resume feature.
Another feature which is often provided on modern electronic speed control systems is commonly referred to as the acceleration feature. The acceleration feature is utilized to automatically increase the desired speed of the vehicle, and consequently the actual speed thereof, by a predetermined amount. Typically, the predetermined amount of increase is relatively small, usually about one mile per hour. For example, if the vehicle operator has set a particular desired speed for the vehicle and the system is engaged for normal operation, the actual speed of the vehicle will be maintained at or near that desired speed. Thereafter, the vehicle operator may wish to increase the actual speed of the vehicle by a small amount. The acceleration feature permits the vehicle operator to increase the actual speed of the vehicle by a predetermined relatively small amount simply by manipulating a single control switch of the system. The resume and acceleration features are desirable not only because they are convenient, but because they cause less distraction to the driver while the vehicle is in motion.